Structure of polymer-matrix conductive film and method for fabricating the same

ABSTRACT

A composite conductive film formed of a polymer-matrix and a plurality of conductive lines less than micro-sized and its fabricating method are provided. The conductive lines are arranged parallel and spaced apart from each other so as to provide anisotropic conductivity. The present conductive film can serve as an electrical connection between a fine-pitch chip and a substrate. Additionally, an adhesive layer is formed on two opposite sides of the conductive film along its conductive direction to increase adhesive areas. The strength and reliability of the package using the conductive film are thus enhanced.

This application is a continuation application of pending U.S.application Ser. No. 10/998,741, filed Nov. 30, 2004 (of which theentire disclosure of the pending, prior application is herebyincorporated by reference).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Z-axis conductive film and a methodfor fabricating the same, and more particularly, the present inventionrelates to a composite conductive film including a polymer matrix andconductive nanowires and a method for fabricating the same.

2. Description of the Related Art

Interconnection technology of a flip-chip package for the I/O pitch lessthan 50 μm (micrometer) is accomplished by Z-axis conductive films.However, Z-axis conductive film cannot be used in a flip-chip packagewith pitch smaller than 30 μm because the size of the conductiveparticles in Z-axis conductive film is approximately 3 μm, and this sizecannot be reduced any further. As a result, Z-axis conductive filmcannot be used in the flip-chip package of the pitch less than 30 μm.The electrical conduction of Z-axis conductive film is realized bycontact between metallic films chemically electroplated on surfaces ofpolymer particles and electrodes of a chip and a substrate. This contactis a kind of physical contact, and has a larger joint resistancerelative to the chemical joint of soldering. Hence, Z-axis conductivefilm is not suitable for integrated circuit devices driven by current.

In addition, joint resistance is related to the density of theconductive particles in conductive film. But the density of theconductive particles in conventional Z-axis conductive film is not veryhigh for the purpose of maintaining insulation in X and Y directions(i.e. avoiding lateral short circuits). As the pitches of the packageddevices become smaller in the future, the electrodes' areas decrease.Joint resistance will be increased as the density of the conductiveparticles is decreased.

In addition to Z-axis conductive film, solder bumps are used toelectrically connect the electrodes of the chip and substrate. Since thecoefficients of thermal expansion (CTE) of the chip and substrate aremismatched, the stress there between adversely influences thereliability of the connection of the chip and the substrate. It isnecessary to use underfill between the chip and the substrate afterpackaging. However, when the jointing pitch is reduced to a size of lessthan 100 μm, the underfill does not easily enter the space between thechip and the substrate. The current methods to resolve this drawbackinclude: (i) replacing the ball-shaped solder bump with a copper studhaving a high height-to-width ratio to increase the gap between the chipand the substrate; and (ii) adapting conductive polymer bumps with lowYoung's modulus to serve as stress buffers. However, the above methodshave disadvantages. The Young's modulus of the copper stud is largerthan that of the solder bump, and is a poor stress buffer. Theresistance of the conductive polymer is at least ten times greater thanthat of metal. Therefore, the conductive polymer is not suitable forelectrical connection of the flip-chip package with fine pitches andsmall electrode areas.

Accordingly, a Z-axis conductive film for electrical connection of afine-pitched flip-chip package was developed. For example, U.S. Pat. No.5,805,426, entitled “Microelectronic Assembles Including Z-AxisConductive Films”, provides a Z-axis conductive film, as shown in FIG.1, which uses a nanoporous polymer film as a template. By filling poresof the polymer film, a composite conductive film formed of nanowires(31, 34, 37) and polymer is provided. The chip and substrate can bedirectly press jointed together by this composite conductive film.Electrical connection there between is established by the metallicnanowires (31, 34, 37) and pads (32, 33, 35, 36) of the chip andsubstrate. The CTE of the composite conductive film can be varied or itsthermal conductivity can be increased by selectively filling differentmetals in the pores of different positions. The nanoporous polymer filmis made by exposing a nonporous resin film to accelerated ion beamhaving sufficient energy or a light beam to pass through the entirethickness of the film. The above method is costly and time-consuming.Moreover, the uniformity of the pore diameters is not easily controlled.The differences of the pore diameters can be as great as hundreds ofnanometers or more. Since the pores of the polymer film are previouslyformed, the polymer film cannot be a B-stage polymer. Thus, the polymerfilm cannot provide sufficient adhesion during a subsequent jointingstep by thermal press to maintain contact between the electrodes of thechip and the substrate and metal nanowires. Thus, the reliability ofelectrical connection of the composite polymer film is degraded.

Additionally, U.S. Pat. No. 5,262,226 provides an Z-axis conductivefilm, as shown in FIG. 2, which includes an alumina substrate 2 having aplurality of metal nanowires 3 formed therein. U.S. Pat. No. 5,262,226thus provides a conductive film 1 made of an alumina substrate 2 andmetal nanowires 3, which is made by two methods. One method involvesselectively undergoing an anodic oxidation process to form a conductivefilm 1 composed of aluminum (Al) 3/alumina (Al₂O₃) substrate 2. Theconductive aluminum 3 can be replaced by solder ball/gold/solder ball.However, this manufacturing method is limited to the capability of aphotolithographic process, and can merely manufacture metal wires with adiameter of 20 μm or more. The other method is firstly to manufacture aporous template of alumina, and then selectively electroplate metal insome of the pores to form a conductive film having a plurality of metalwires. Thereafter, one electrode is respectively formed at the upper andlower ends of each metal wire to joint a substrate-level chip. Alumina(Al₂O₃) is used as a substrate of the conductive film 1 of U.S. Pat. No.5,262,226. Alumina has good heat-dissipation and insulating properties,but its Young's modulus is too large and too fragile to release stressgenerated during packaging. Moreover, the adhesion between alumina andthe substrate, as well as between alumina and the chip is insufficientto maintain electrical connection of the electrodes and the conductivefilm.

Accordingly, the intention is to provide a Z-axis conductive film withfine pitches, low resistance and high jointing strength, which canovercome the drawbacks of the prior art.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a structure ofpolymer-matrix conductive film and a method for fabricating the same,which is suitable for electrical connection between a fine-pitched chipand a fine-pitched substrate.

A second objective of the present invention is to provide a sandwichedpolymer-matrix conductive film and a method for fabricating the same,which can provide a Z-axis conductive film with a larger adhesive areato strengthen the package of a semiconductor device.

A third objective of the present invention is to provide a structure ofanisotropic polymer-matrix conductive film and a method for fabricatingthe same, which can provide an input/output redistribution function inorder that the current substrate can be applied to a package offine-pitched chip in the future.

In order to attain the above objectives, the present invention providesa polymer-matrix conductive film, which includes a polymer-matrixconductive body having unidirectional conductivity, a plurality ofconductive lines arranged parallel and spaced apart from each other anda polymer material filled in spacings of the conductive lines. Anadhesive layer is respectively formed on two opposite sides of thepolymer-matrix conductive body along the direction of conductivity.Hence, a sandwiched polymer-matrix conductive film is provided.

A larger adhering area is provided between the chip and the substrate bythe sandwiched polymer-matrix conductive film. The portions of the chipand the substrate, except for their electrodes, are jointed with thepolymer-matrix conductive film by the adhesive layer so as to enhancethe package strength of the semiconductor device.

In another aspect, the present invention provides a method forfabricating a polymer-matrix conductive film, which comprises providinga template having a plurality of holes arranged parallel and spacedapart from each other and an electrode provided on one end of the holes;filling a first conductive material in the holes of the template overthe electrode; filling a magnetic material in the holes on the firstconductive material; removing the template to form a plurality ofdouble-layered conductive lines arranged parallel and spaced apart fromeach other; applying a magnetic field upon the double-layered conductivelines and filling a polymer material in spacings of the double-layeredconductive lines; and removing the electrode, a portion of the polymermaterial and the magnetic material to form the polymer-matrix conductivefilm with a plurality of conductive lines arranged parallel and spacedapart from each other.

The present method can manufacture a composite conductive film having apolymer matrix and a plurality of conductive lines less than nanometersformed therein, which is suitable for electrical connection between thechip and the substrate with fine pitches.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will be better understood with regard to the followingdescription, appended claims and accompanying drawings that are providedonly for further elaboration without limiting or restricting the presentinvention, where:

FIG. 1 is a schematic cross-sectional view of a conventional package ofa semiconductor device utilizing a known Z-axis conductive film as anelectrical connection;

FIG. 2 is a schematic cross-sectional view of another known Z-axisconductive film;

FIGS. 3A through 3F are schematic cross-sectional views of apolymer-matrix conductive film corresponding to various stages of thepresent method according to a first preferred embodiment of the presentinvention;

FIGS. 4F to 4G are schematic cross-sectional views of a polymer-matrixconductive film corresponding to the last two steps of the presentmethod according to a second preferred embodiment;

FIGS. 5F to 5G are schematic cross-sectional views of a polymer-matrixconductive film corresponding to the last two steps of the presentmethod according to a third preferred embodiment;

FIG. 6F is a schematic cross-sectional view of a variance of the presentpolymer-matrix conductive film;

FIG. 6G is a schematic cross-sectional view of another variance of thepresent polymer-matrix conductive film;

FIG. 7 is a schematic cross-sectional view of a package of asemiconductor device utilizing the polymer-matrix conductive film of thefirst preferred embodiment;

FIG. 8 is a schematic exploded view of a package of a semiconductordevice utilizing the polymer-matrix conductive film of the thirdpreferred embodiment; and

FIG. 9 is a schematic cross-sectional view of a package of asemiconductor device utilizing the polymer-matrix conductive films ofFIGS. 6F and 6G.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a universal Z-axis conductive film, whichcomprises a polymer matrix and a plurality of conductive lines less thanmicro-sized. The present Z-axis conductive film is suitable for apackage of a semiconductor device in 45 nm technology node. The polymermatrix can be made of a material with a low Young's modulus to aid as astress buffer during the subsequent packaging of the semiconductordevice. In addition, the structure and composition of the conductivelines can be varied such that the present Z-axis conductive film canconnect electrically with the chip and the substrate by bonding. Thejointing resistance can thus be lowered.

However, it is necessary to keep Z-direction parallel of the conductivelines so as to maintain good insulation of the present Z-axis conductivefilm in X-Y directions. However, the diameter of the currently-usedconductive lines is approximately 200 nm (nanometers) or less and theirlength is 10 μm (micrometers) or more. The height-to-width ratio of theconductive lines is high, and thus the conductive lines are easilyinclined when subjected to external force. The polymer matrix ispreferably made of a thermosetting polymer with a glass transitiontemperature (T_(g)) higher than 250° C. Moreover, an adhesive layer canbe formed respectively on two jointing surfaces of the presentpolymer-matrix conductive film to enhance jointing strength between thechip and the substrate, and also increasing insulation of the presentZ-axis conductive film in X-Y directions.

More specifically, the present polymer-matrix conductive film is a kindof composite film having a polymer matrix and a plurality of nanowiresformed therein. The nanowires are made of a low resistance metal andinactive for oxidation, such as gold and silver. Multi-layered metallines containing solder can be used as the nanowires for bonding to theelectrodes of the substrate and chip. The polymer matrix can be made ofa thermosetting polymer with T_(g) higher than 250° C. and a low Young'smodulus to maintain the nanowires parallel in the vertical direction andbuffer the stress generated during the jointing of the chip and thesubstrate.

The upper and lower surfaces of the nanowires/polymer matrix compositefilm can also be respectively coated with an adhesive layer in orderthat the portions of the chip and the substrate, except for theirelectrodes, joint with the polymer-matrix conductive film by theadhesive layer, increasing the adhering area and thus strengthening thepackage.

The present polymer-matrix conductive film and the method forfabricating the same will be described in detail according to thefollowing preferred embodiments with reference to accompanying drawings.

FIGS. 3A through 3F are schematic cross-sectional views of apolymer-matrix conductive film corresponding to various stages of thepresent method according to a first preferred embodiment of the presentinvention. Referring to FIG. 3A, initially, a template 300 is provided.The template 300 includes a plurality of holes 301 arranged parallel andspaced apart from each other and an electrode 302 is provided at one endof the holes 301. In the first preferred embodiment, the template 300can be a template of alumina (Al₂O₃) with pores of a size less than 200nanometers. The electrode 302 can be made of a high conductive material,such as gold or silver. Next, referring to FIG. 3B, a first conductivematerial 303 is filled in the holes 301 over the electrode 302. Then, amagnetic material 304 is filled in the holes 301 on the first conductivematerial 303. Double-layered nanowires are provided. In the firstpreferred embodiment, the first conductive material 303, such highconductive gold or silver, and the magnetic material 304, such as cobaltor nickel, can be sequentially filled in the holes 301 by electroplatingto form double-layered metal nanowires. Thereafter, the template 300 isremoved to form a plurality of double-layered conductive lines 303 and304 arranged parallel and spaced apart from each other, such asdouble-layered metal wires of gold (silver) 303/cobalt (nickel) 304.Subsequently, referring to FIGS. 3C and 3D, a magnetic field 305 isapplied to the double-layered conductive lines 303 and 304. By applyingthe magnetic field 305, a polymer material 306 is filled in the spacingsof the double-layered conductive lines 303 and 304 for example bydiffusion. The polymer material 306 can be made of a thermosettingpolymer with a low Young's modulus, such as epoxy resin or polyimide, tomaintain the double-layered conductive lines 303 and 304 parallel duringsubsequent manufacturing processes and serve as a stress buffer whenpackaging the semiconductor device. Moreover, in the first preferredembodiment, the interaction between the magnetic field 305 and themagnetic material 304 helps to maintain the Z-directionality and thedouble-layered conductive lines 303 and 304 parallel after removing thetemplate 300 and during the filling of the polymer material 306.Additionally, before filling the polymer material 306, it is preferableto use a long chain organic acid to modify the surfaces of thedouble-layered conductive lines 303 and 304 to become more hydrophobicsurfaces for facilitating the flow in of the polymer material 306.Thereafter, the baked polymer material 306 is hardened. Next, referringto FIG. 3E, a portion of the polymer material 306 and magnetic material304 is polished and the electrode 302 is removed. As a consequence, thepolymer-matrix conductive film 30 with a plurality of conductive lines303 arranged parallel and spaced apart from each other is provided. Thusthe polymer-matrix conductive film 30 has a Z-directional conductivity.Finally, referring to FIG. 3F, an adhesive layer 307, preferably aB-stage polymer, is coated respectively on two opposite sides of thepolymer-matrix conductive film 30 across the direction of conductivity.A sandwiched polymer-matrix conductive film is provided, which increasesthe adhering area between the chip and the substrate and the jointingstrength there between is enhanced.

FIGS. 4F to 4G are schematic cross-sectional views of the presentpolymer-matrix conductive film corresponding to the last two steps ofthe present method according to a second preferred embodiment of thepresent invention. The former several steps of the second preferredembodiment are the same as those steps of the first preferred embodimentcorresponding to drawings of FIGS. 3A to 3E. In a step corresponding toFIG. 4F, a barrier layer 407 and a solder ball 408 are sequentiallyformed on two opposite ends of the conductive lines 403 of thepolymer-matrix conductive film to form a polymer-matrix conductive film40 with multi-layered conductive lines. The multi-layer conductive lines403 are arranged parallel and spaced apart from each other to provideunidirectional conductivity. When the conductive lines 403 of thepolymer-matrix conductive film 40 are made of gold, the barrier layer407 between the conductive lines 403 and solder balls 408 can be made ofnickel. Hence, the polymer-matrix conductive film 40 can bond to theelectrodes of the substrate and the chip. Subsequently, referring toFIG. 4G, an adhesive layer 409, preferably of a B-stage polymer, isrespectively coated on the two opposite sides of the polymer-matrixconductive film 40 along the direction of conductivity to form thesandwiched polymer-matrix conductive film.

FIGS. 5F to 5G are schematic cross-sectional views of the presentpolymer-matrix conductive film corresponding to the last two steps ofthe present method according to a third preferred embodiment of thepresent invention. The former several steps of the third preferredembodiment are the same as those steps of the first preferred embodimentcorresponding to the drawings of FIGS. 3A to 3E. A polymer-matrixconductive film 506 with a plurality of conductive lines 503 arrangedparallel and spaced apart from each other is first provided. In a stepcorresponding to the drawing of FIG. 5F, a plurality of conductive pads507 are formed on one side of the polymer-matrix conductive film alongthe direction of conductivity to serve as an electrical connection withthe electrodes of the chip in the subsequent packaging process. Next, adielectric layer 508 is formed on the other side of the polymer-matrixconductive film along the direction of conductivity. A plurality ofopenings 509 are then formed in the dielectric layer 508. Afterward, asecond conductive material is filled in the openings 509 to form aconductive redistribution layer 510 under the dielectric layer 508. Theconductive redistribution layer 510 is used as an electrical connectionwith the electrodes of the substrate. Thus, in the third preferredembodiment, the conductive redistribution layer 510 is formed on thejointing surfaces between the polymer-matrix conductive film and thesubstrate to enlarge input/output (I/O) pitches of the polymer-matrixconductive film for electrical connection with the substrate. When theI/O pitches of the chip become smaller in the future, the currently usedorganic substrate can still be electrically connected with the chip bythe polymer-matrix conductive film of the third preferred embodiment.Briefly, this polymer-matrix conductive film provides the functions ofvertical electrical connection and I/O redistribution such that themanufacturing process of the current substrate can be integrated withthe packaging of chips having fine pitches in the future. Subsequently,referring to FIG. 5G, an adhesive layer 511 is respectively formed onthe conductive pads 507 and under the conductive redistribution layer510.

FIG. 6F is a schematic cross-sectional view of the presentpolymer-matrix conductive film corresponding to the last step of thepresent method according to a fourth preferred embodiment of the presentinvention. The former several steps of the fourth preferred embodimentare the same as those steps of the first preferred embodimentcorresponding to the drawings of FIG. 3A to FIG. 3E. A polymer-matrixconductive film 606 with a plurality of conductive lines 603 arrangedparallel and spaced apart from each other is first provided. In a stepcorresponding to FIG. 6F, a plurality of conductive pads 604 a areformed on one side of the polymer-matrix conductive film 606 along thedirection of conductivity. Next, an adhesive layer 605 is respectivelyformed on the other side of the polymer-matrix conductive film 606 alongthe direction of conductivity and under the conductive pads 604 a.

FIG. 6G is a variance of the polymer-matrix conductive film of FIG. 6F.In FIG. 6G, the pitches of the conductive pads 604 b on one side of thepolymer-matrix conductive film 606 are enlarged such that the pitches ofthe conductive pads 604 b are larger than those of the conductive pads604 a. When the two polymer-matrix conductive films 606 are stacked, theconductive pads 604 a and 604 b partially overlap. Hence, by stackingthe polymer-matrix conductive films 606 of FIGS. 6F and 6G to make theconductive pads 604 a and 604 b partially overlap, conductive layerredistribution can be attained and an enlargement of the I/O pitches ofthe polymer-matrix conductive film is obtained.

By stacking multiple layers of the polymer-matrix conductive films eachof which have conductive pads with respective different pitches,conductive layer redistribution can be obtained, and an enlargement ofthe I/O pitches of the polymer-matrix conductive film is attained suchthat the manufacturing process of the current substrate can beintegrated with the future packaging of chips with fine pitches.

The present invention also provides various packages of semiconductordevices utilizing the present polymer-matrix conductive films. FIG. 7 isa schematic cross-sectional view of the package of the semiconductordevice utilizing the polymer-matrix conductive film of the firstpreferred embodiment (referring to FIG. 3F) to serve as electricalconnection between the chip 701 and the substrate 702. The substrate 702has a circuit pattern (not shown) and a plurality of electrodes (firstpads) 704 electrically connected to the circuit pattern. The electrodes(second pads) 703 of the chip 701 and the electrodes 704 of thesubstrate 702 are respectively electrically connected with the two endsof the conductive lines 306 of the polymer-matrix conductive film bythermal press. Therefore, electrical connection between the chip 701 andthe substrate 703 is established. As to the portions of the chip 701 andsubstrate 702, except for the electrodes 703 and 704, which are jointedwith the polymer-matrix conductive film by the adhesive layers 307, theadhering area is larger and the strength of the package is thusenhanced.

FIG. 8 is a schematic exploded view of a semiconductor device package 80utilizing the polymer-matrix conductive film 506 (referring to FIG. 5G)of the third preferred embodiment to serve as electrical connectionbetween the chip 801 and the substrate 802. The substrate 802 has acircuit pattern and a plurality of electrodes (first pads) 804 withlarger I/O pitches electrically connected to the circuit pattern. Theelectrodes (second pads) 803 of the chip 801 are electrically connectedto the conductive pads 507 of the polymer-matrix conductive film. Theelectrodes 804 of the substrate 802 are electrically connected to theconductive redistribution layer 510 of the polymer-matrix conductivefilm 506. As to the portions of the chip 801 and the substrate 802,except for the electrodes 803 and 804, which are jointed with thepolymer-matrix conductive film 506 by the adhesive layer 511. Since theconductive redistribution layer 510 can enlarge the I/O pitches of thepolymer-matrix conductive film 506 electrically connected to thesubstrate 506, the current-used substrate can be integrated with theflip-chip package with fine pitches in the future.

FIG. 9 is a schematic cross-sectional view of a package of asemiconductor device utilizing the polymer-matrix conductive film 606(referring to FIG. 6F) and its variance (referring to FIG. 6G) to serveas an electrical connection between the chip 901 and the substrate 902.The substrate 902 has a circuit pattern and a plurality of electrodes904 with larger I/O pitches electrically connected to the circuitpattern. The electrodes 903 of the chip 901 are electrically connectedto one end of multiple conductive lines 603 of the polymer-matrixconductive film 606. The polymer-matrix conductive films 606 of FIGS. 6Fand 6G are stacked together such that the conductive pads 604 a and 604b partially overlap. The conductive pads 604 a are directly electricallyconnected to one end of the multiple conductive lines 603 of thepolymer-matrix conductive film adjacent thereto. The conductive pads 604b are directly electrically connected to the electrodes 904 of thesubstrate 902. As to the portions of the chip 901 and substrate 902,except for the electrodes 903 and 904, which are jointed with thepolymer-matrix conductive film by the adhesive layers 605. In thepackage of FIG. 9, conductive layer redistribution is obtained bystacking multiple polymer-matrix conductive films 606, each of which hasrespective conductive pads 604 a and 604 b, with different pitches. Thepurpose of enlarging the I/O pitches of the polymer-matrix conductivefilm is attained. The currently used substrate thus can be integratedwith the future flip-chip package with fine pitches.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments thereof, those skilledin the art can easily understand that all kinds of alterations andchanges can be made within the spirit and scope of the appended claims.Therefore, the spirit and scope of the appended claims should not belimited to the description of the preferred embodiments containedherein.

1. A polymer-matrix conductive film, comprising: a polymer-matrixconductive body with unidirectional conductivity, including a pluralityof solid conductive nanowires arranged parallel and spaced apart fromeach other and a polymer material filled in the spaces between the solidconductive nanowires; and an adhesive layer on each of two oppositesides of said polymer-matrix conductive body across the direction ofconductivity.
 2. The polymer-matrix conductive film of claim 1, whereinsaid polymer material is a thermosetting polymer having a glasstransition temperature (Tg) higher than a temperature for a thermaljoint process.
 3. The polymer-matrix conductive film of claim 2, whereinsaid adhesive layer includes a B-stage polymer.
 4. The polymer-matrixconductive film of claim 1, wherein said adhesive layer includes aB-stage polymer.
 5. The polymer-matrix conductive film of claim 1,wherein each of said solid conductive nanowires has an aspect rationequal to or larger than
 50. 6. The polymer-matrix conductive film ofclaim 1, wherein said solid conductive nanowires are arranged paralleland spaced apart from each other with a pitch not more than 1 μm.